In the field of transduction, actuators are used to apply a force to a surface. In high performance applications where size and weight are at a premium, this type of actuator requires a high-power transfer efficiency. Such applications include, for example, sonar transmitters or projects, vibration control actuators, micropositioners, valves, deformable mirrors, and linear motors.
Electrostrictive or piezoelectric actuators occasionally have been employed in these applications. Such actuators, fabricated for example of disc components made of lead-magnesium-niobate ceramic system (PMN), are especially useful because of their excellent transduction characteristic.
The typical PMN actuator design of the prior art has not, however, taken advantage of the full work output of the electrostrictive elements for low drive voltages. Attempts to increase output have not been successful. For low-frequency broadband applications, efficient utilization of the material requires directly coupled amplifiers, as transformer-coupled amplifiers are typically large and heavy. Maximum output from a PMN element, for example, requires that the drive voltage be comparable to the element's breakdown voltage.
In efforts to increase the performance of PMN electrostrictive actuators, little attention has been given to the optimizing of the multi-wafer structure particularly to maximize stiffness and the critical role which the production process plays.
More specifically, since the maximum practical direct coupled drive voltage is on the order of 1000 volts and typical breakdown voltages are 50 volts per mil, it follows that the drive element ought to be as thin as possible, such as 0.020 mils or less in thickness. In order, therefore, to achieve a large power output, large stacks containing on the order of 100 elements are built. Heretofore, the fabrication of these stacks has been directed to end uses in displacement applications. For high power coupling efficiency, both the force and the displacement need to be high.
Thus, in order to realize a given force output from thin wafers the deleterious effects of slicing the bulk material into thin wafers and the consequent interface stiffness in a stack must be overcome. Further, in order to achieve the optimum power output, high stack stiffness as well as large cross-sectional area are required.